Timing arrangement for use in cameras adapted to be used for making long exposures

ABSTRACT

A photographic camera can be used for making long exposures of the type requiring the user to effect opening of the shutter and then to positively effect closing of the shutter after the elapse of an appropriate exposure time. A timing arrangement which notifies the user when to close the shutter comprises an energystoring element, and supply means for supplying energy to the energy storing element. A photosensitive element, exposed to scene light, controls the rate of change of energy stored by the energy-storing element as a function of scene brightness, after the shutter has been opened, and permits the amount of energy stored by the energy-storing element to reach a predetermined value corresponding to a predetermined total amount of light impingement on the photosensitive element. An electronic threshold detector, connected with the energy-storing element and having an output, produces at its output a control signal only when the energy stored by the energy-storing element has reached the aforesaid predetermined value. An electrical signalling unit, such as a lamp or buzzer, is connected to the output of the threshold detector, and furnishes to the user of the camera a readily observable timing signal in response to generation by the threshold detector of the aforementioned control signal, thus notifying the user that closing of the shutter should be effected.

llite Wagner tes 11 1 'llMllNG ARRANGEMENT FOR USE EN CAMERAS ADAPTED T018E USED FOR MAKiNG LONG EXFOSURES [75] Inventor: Karl Wagner,Ottobrunn, Germany [73] Assignee: Agfa-Gevnert Ahtiengesellschnft,

Leverkusen, Germany [22] Filed: June 14, 11972 [21] Appl. No.: 262,725

[30] Foreign Application Priority Data June 18, 1971 Germany P 21 30197.3

[52] U.S. Ci. 95]) C, 95/10 CE, 95/l0 CT, 95/53 EB [51] int. Cl. 603i:7/08, 60% 9/08 [58] Field of Search 95/10 C, 10 CT, 10 CE, 95/53 EB [56]References Cited UNlTED STATES PATENTS 3,581,634 6/1971 on .Q 95/10 CT3,636,84l 1/1972 Wagner 95/10 CT Primary Examiner--Samuel S. MatthewsAssistant ExaminerRussell B. Adams, Jr. Attorney-Michael S. Striker [57]AETRACT A photographic camera can be used for making long exposures ofthe type requiring the user to effect opening of the shutter and then topositively effect closing of the shutter after the elapse of anappropriate exposure time. A timing arrangement which notifies the userwhen to close the shutter comprises an energy-storing element, andsupply means for supplying energy to the energy storing element. Aphotosensitive element, exposed to scene light, controls the rate ofchange of energy stored by the energy-storing element as a function ofscene brightness, after the shutter has been opened, and permits theamount of energy stored by the energystoring element to reach apredetermined value corresponding to a predetermined total amount oflight impingement on the photosensitive element. An electronic thresholddetector, connected with the energystoring element and having an output,produces at its output a control signal only when the energy stored bythe energy-storing element has reached the aforesaid predeterminedvalue. An electrical signalling unit, such as a lamp or buzzer, isconnected to the output of the threshold detector, and furnishes to theuser of the camera a readily observable timing signal in response togeneration by the threshold detector of the aforementioned controlsignal, thus notifying the user that closing of the shutter shouldbeeffected.

8 Claims, 1 Drawing Figure martinis TlMlNG ARRANGEMENT lFOlll USE llNCAMERAS ADAPTED TO BE USED lFOlR lVllAlKllNG LONG EXPOSURES BACKGROUNDOF THE INVENTION The present invention relates to photographic camerasand particularly to cameras having provision for the taking of so-calledlong exposures. A long exposure must be taken, for example, when theavailable scene light is so low as to require a longer exposure timethan can be provided by the automatic shutter-timing mechanism of thecamera. In such event, the user of the camera himself must not onlyeffect shutter opening, but activation of the shutter-release mechanism,but must also positively effect shutter closing, after an elapse of anappropriate exposure time. The invention relates to means for assistingthe user of the camera in selecting themoment of shutter closing.

Commonly owned U.S. Pat. No. 3,636,841 discloses an arrangement of thetype in question. That arrangement includes a moving-coil instrumenthaving an indicating needle which is movable to coincidence with acertain dial marking. When the camera is used for taking long exposures,a capacitor is charged through a photoresistor, and the increasingcapacitor voltage effects a continuous sweeping movement of theindicating needle of the moving-coil instrument. When the user of thecamera decides that the needle is properly coincident with the aforesaiddial marking he effects shutter closing.

The arrangement of the aforementioned U.S. Pat. has the disadvantagethat it requires of the user of the cameratoo much subjective judgement,because of the necessarydecision as to whether proper coincidence withthe needle with the dial marking has been achieved. The decision is notparticularly easy, because the range of movement of the needle is ofcourse quite small. Farsighted persons, for example, have difficulty indetecting the exact moment of coincidence.

The use of a moving-coil instrument as the exposuretime signaller in theaforementioned U.S. Pat. was motivated by a desire to increase theusefulness of the moving-coil instrument which was anyway provided tomonitor scene brightness. However, and as just explained, the additionalpurpose of notifying the user that the shutter should be closed is notadequately achieved.

SUMMARY OF THE lNVENTlON It is accordingly the general object of thepresent invention to overcome such disadvantages as described above.

It is a more particular object to provide a novel and improved timingaid which overcomes such disadvantages.

it is a further object to provide a timing aid which abruptly generatesa timing signal readily observable by the user of the camera, at themoment when the user should effect closing of the shutter.

It is another object to provide such a timing aid which takes intoaccount the finite response time of a human user responding to suchtiming signal.

These objects, and others which will become clearer hereafter, can forinstance be met by an arrangement which comprises a shutter,energy-storing means, and supply means for supplying energy to theenergystoring means. Photosensitive means, exposed to scene light,controls the rate of change of energy stored by the energy-storing meansas a function of scene brightness and in response to opening of theshutter, and permits the amount of energy stored by the energy-storingmeans to reach a predetermined value corresponding to a predeterminedtotal amount of light impingement on the photosensitive means. Athreshold-detector, connected with the energy-storing means and havingan output, produces at such output a control signal, when and only whenthe energy stored by the energy-storing means has reached theaforementioned predetermined value. lmportantly, electric signallingmeans, connected to the output of the threshold-detector, furnishes tothe user of the camera an abrupt and readily observable timing signal inresponse to generation by the threshold-detector of the aforementionedcontrol signal, thus notifying the user that closing of the shuttershould be effected.

The electrical signalling means can for instance be a signal lamp whichis illuminated for a brief moment when the user is to be notified thatthe shutter should be closed. Alternatively, the lamp can be illuminateduntil such time as the shutter is actually closed, or the lamp can beilluminated at the moment the shutter is opened and then becomeextinguished at the moment the user should effect closing of theshutter. Other variations are possible. I a

The electrical signalling means can be a light emitting diode although amoving-coil instrument can also be used. It is also possible to employ amoving-coil instrument as a light-meter instrument, e.g., to determinewhether the scene light is sufficient for automatic exposures or whetherso low as to necessitate the use of a tripod and a long exposure. Thesignalling means could then be a signal lamp, and the timing arrangementcould comprise a capacitor charged via a photoresistor exposed to scenelight. For the sake of simplicity, the same photoresistor can be usedboth for taking readings with the moving-coil instrument of scene light,and also can be used with the signal lamp during the making of longexposures with a tripod as a timing aid. Also for the sake ofsimplicity, the moving-coil instrument can be left in circuit with thephotoresistor during the timing operation performed by the timingarrangement during the making of a long exposure, providing the internalresistance of the moving-coil instrument is negligible compared to thatof the photoresistor, at least when the intensity of the impinging lightis low i.e., so that the presence of the moving-coil instrument will notdistort the charging operation of the capacitor in the long exposuremode.

There are severalmanners in which change of energy stored by thecapacitor (or other energy-storing element) is used for timing purposes.it is particularly advantageo'us to short-circuit the capacitor prior toopening of the shutter, and then at the time of shutter opening connectthe capacitor to a charging battery and in series with thephotoresistor. Alternatively, however, the capacitor might be initiallycharged at the time of shutter opening, and then permitted to dischargeto a lower voltage to effect activation of the signal lamp, or othersignalling unit. Also, the energy-storing means need not be a simplecapacitor, but could be another energy-storing element.

For the sake of simplicity, it would for instance be possible to avoidcumbersome switching operations, by permitting the signal lamp tobriefly light up when other than long exposures are being made i.e.,dur- .ing automatic daylight operation, or when a flash unit isemployed. However, prolonged furnishing of a signal, whether anillumination or an extinguishing, would be provided, as one possibility,only when the signal lamp is being used as a timing aid for the takingof long exposures with a tripod, etc.

Because the response time of the operator is finite, it is contemplatedfor example to provide a photoresistor whose resistance decreases withincreasing light intensity, and which decreases to a higher extent whenthe impinging light is already quite low i.e., under lighting conditionswhich requirethe taking of long exposures. In this way the signal lampwill be illuminated slightly ahead of time, to compensate for theresponse time of the human user.

The novel features which are considered as characteristics for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method'ofoperation, together with additional objects and advantages thereof, willbe best understood'from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE illustrates insomewhat schematic form one embodiment according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS One of the blades 5 of ashutter is pivotable about an axis 6 between positions in which theshutter is open and in which the shutter is closed. Blade 5 has astepped portion 5a upon which rests the median contact 1b of a two-wayswitch 1. The springiness of median contact lb normally urges it intocontact with contact 1c. However, when the shutter is closed, asdepicted in the FIGURE, the shutter blade 5 forces the median blade 1binto engagement with contact la.

When the shutter is closed, contacts la, 1b are in engagement andtogether close a series circuit composed of battery 2, photoresistor 3and moving-coil instrument 4. Photoresistor 3 is exposed to scene light,and the intensity of such light determines the resistance value of theresistor, and thus the amount of current flow in the coil of indicator4. Accordingly, the indicating needle of indicator 4 will move to aposition indicative of the scene brightness.

Indicator 4 indicates to a user whether or not the scene brightness isso low as to require the taking of a long exposure. If the need for along exposure is indicated, the user will in conventional manner set thecamera to 8" operation i.e., to a position permitting the user to selectboth the time of shutter opening and the time of shutter closing. Thus,for instance, when the user presses down the shutter-release button, hewill hold it down to maintain the shutter open and then release thebutton to permit the shutter to close.

Opening of the shutter involves movement downwards of illustrated blade5, and electrical engagement between contacts lb and 10. It will benoted that when contacts la, lb are engaged the capacitor 8 isshortcircuited and cannot store energy. However, when con tacts lb, 1cengage, the capacitor 8 is connected in series with battery 2,photoresistor 3 and moving-coil instrument 4. According to well knownprinciples, the capacitor 8 will tend to charge to the voltage ofbattery 2 and at a rate which is a function of the resistance ofphotoresistor 3, and which is thus a function of scene brightness. Forthe sake of simplicity, and to avoid the provision of further switches,indicator 4 which is not actually needed during the taking of the longexposure is kept in the circuit, because its internal resistance isnegligible compared to that of photoresistor 3 when light of lowintensity impinges on the photoresistor.

Connected directly across capacitor 8 is an electronicthreshold-detector 9, whose internal circuitry can be of any of theextremely well known types, such as for instance a Schmitt trigger. Whenthe capacitor 8 charges up to a voltage corresponding to the thresholdtriggering voltage of threshold-detector 9, detector 9 produces anoutput signal at its output c, d which effects illumination of signallamp 10. The values of photoresistor 3, capacitor 8, and the triggervoltage of unit 9 are so chosen, that capacitor 8 reaches the triggervoltage at the time that the film being exposed has been exposed to apredetermined total amount of light. Clearly, during the film exposuretime, if the scene brightness suddenly increases, the resistance ofresistor 3 will decrease resulting in faster charging of capacitor 8 andearlier reaching of the threshold value, corresponding to the presumedfaster exposure of the film actually being exposed.

When the threshold voltage has been reached by capacitor 8, the lamp 10is illuminated and remains illuminated until the shutter-control buttonis released to cause closing of the shutter. At the moment of shutterclosing, blade 5 restores the engagement of contacts lb, 1c, shortingand thereby discharging the capacitor 8 and immediately causing thecapacitor voltage to drop below the threshold value necessary tomaintain lamp 10 illuminated.

Provision of graduated light-obstructing filter 11 in front of thephotoresistor 3 i.e., between the resistor 3 and the impinging lightpermits adjustment of the timing operation as a function of differentfilm sensitivities and/or different aperture sizes. For instance, if amore sensitive film is used requiring less total light fall to effectproper exposure, an adjusting ring (not shown) can be turned to asetting corresponding to such more-sensitive film. This would result inturning of graduated filter 11 to a position in which a more translucentportion of the filter is placed in the light path of resistor 3.Accordingly, resistance value of resistor 3 will be lower, and thecharging time of capacitor 8 will be shortened in correspondence withthe decreased exposure time needed for the more sensitive film. Asimilar relationship applies to an adjustment of the filter position asa function of selected aperture size, or other parameters.

The operation of the illustrated arrangement should be apparent fromwhat has already been said:

When a photograph is to be taken, the user of the camera closes a(non-illustrated) switch which applies the battery voltage to the seriesconnection of components 3, 4 and causes indicator 4 to indicate thescene brightness. If the scene brightness is sufficient for automaticshutter control, the user presses the shutter button to effect shutteropening and the shutter is automatically closed after an appropriateexposure time.

However, if indicator 4 indicates light intensity so low as to requirean exposure time exceeding the longest possible automatic exposure time,the user sets the camera in conventional manner for B operation.Thereupon, the user will for instance set the aperture size inconventional manner, thereby effecting a corresponding turning ofgraduated filter 11. The user presses the shutter-control button openingthe shutter, and holds the button down to maintain the shutter open.When the capacitor 8 has charged to the predetermined threshold voltageof threshold-detector 9, lamp 10 lights up, notifying the, user that heshould now permit the shutter to close. When the shutter is closed, thecapacitor 8 is short-circuited. and the lamp 111 is extinguished.

To account for the finite response time of the human user, it is ofadvantage to select a photoresistor whose light versus resistancecharacteristic has a first steepness of the part of the characteristiccorresponding to high intensity of light, and a different steepness atthe part of the characteristic curve corresponding to lower intensitylight i.e., to the low intensity light prevailing during andnecessitating the taking of long exposures. For instance, the resistancevalue of resistor 3, when the light intensity is quite high, couldincrease with decreasing light at a certain rate, and increase withdecreasing light at a higher rate when the light intensity is quite lowi.e., of such low intensity as to necessitate long exposure times.

It hardly need be mentioned that the camera can also have provision forthe taking of photographs using a flash unit, and of course it can beprovided with means for mounting the camera on a tripod, and can beprovided with any of the conventional remote-control shutter-activatedarrangements known, for instance those incorporating a cable leading tothe camera.

Likewise, it is also possible to use other switching means in place ofthe two-way switch 1 shown. Such other switch means could establish thenecessary connection between the illustrated or equivalent components ina different fashion. Furthermore, the mechanical switching means neednot be coupled to the actual shutter blade, but can also be coupled tothe shutteractivating mechanism, e.g., to the linkage between theshutter-control button and the shutter blades.

it will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions and circuits differing from the types described above.

While the invention has been illustrated and described as embodied in aphotographic camera having provision for the taking of long exposures,it is not in tended to be limited to the details shown, since variousmodifications and structural changes may be made without departing inany way from the spirit of the present invention.-

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can be applying current knowledge,readily adapt it for various applications withoutomitting features that,from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning I and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. In combination with a photographic camera of the type which can beused to make long exposures and which includes means which must bepositively actuated by the user to effect opening of the shutter andthereafter positively actuated by the user to effect closing of theshutter after the elapse of an appropriate exposure time, a timingarrangement for assisting the user in such non-automatic operation ofthe shutter, comprising, energy-storing means; supply means forsupplying energy to said energy-storing means; photosensitive meansexposed to scene light and operative in response to opening of saidshutter for changing the amount of energy stored in said energy-storingmeans at a rate dependent upon scene brightness and permitting theamount of energy stored by said energy-storing means to reach apredetermined value corresponding to a predetermined cummulative totalamount of light impinging upon said photosensitive means; electronicthreshold detector means, connected with said energy-storing means andhaving an output, for producing at said output a control signal onlywhen the energy stored by said energy-storing means has reached saidpredetermined value; and electrical signalling means connected to saidoutput of said electronic threshold detector means and operative forfurnishing to the user of the camera a readily observable timing signalin response to generation by said electronic threshold detector means ofsaid control signal, thus notifying the user that closing of saidshutter should be effected.

2. An arrangement as defined in claim 1, wherein said electricalsignalling means comprises an illuminable lamp.

3. An arrangement as defined in claim 1, wherein said electricalsignalling means comprises a light emitting diode.

4. An arrangement as defined in claim 1, and further including switchmeans for connecting said energystoring means in circuit with saidsupply means and said photosensitive means in response to opening ofsaid shutter.

5. An arrangement as defined in claim 4, wherein said switch means ismechanically connected with said shutter.

6. An arrangement as defined in claim 4, wherein said switch means ismechanically connected with the shutter-activating means.

7. An arrangement as defined in claim 1, wherein said photosensitivemeans comprises a photoresistance whose resistance decreases withincreasing intensity of impinging light and at a lesser rate when thelight intensity is higher and at a higher rate when the light intensityis lower.

8. An arrangement as defined in claim 1, wherein said energy-storingmeans comprises a capacitor.

1. In combination with a photographic camera of the type which can beused to make long exposures and which includes means which must bepositively actuated by the user to effect opening of the shutter andthereafter positively actuated by the user to effect closing of theshutter after the elapse of an appropriate exposure time, a timingarrangement for assisting the user in such non-automatic operation ofthe shutter, comprising, energystoring means; supply means for supplyingenergy to said energystoring means; photosensitive means exposed toscene light and operative in response to opening of said shutter forchanging the amount of energy stored in said energy-storing means at arate dependent upon scene brightness and permitting the amount of energystored by said energy-storing means to reach a predetermined valuecorresponding to a predetermined cummulative total amount of lightimpinging upon said photosensitive means; electronic threshold detectormeans, connected with said energystoring means and having an output, forproducing at said output a control signal only when the energy stored bysaid energystoring means has reached said predetermined value; andelectrical signalling means connected to said output of said electronicthreshold detector means and operative for furnishing to the user of thecamera a readily observable timing signal in response to generation bysaid electronic threshold detector means of said control signal, thusnotifying the user that closing of said shutter should be effected. 2.An arrangement as defined in claim 1, wherein said electrical signallingmeans comprises an illuminable lamp.
 3. An arrangement as defined inclaim 1, wherein said electrical signalling means comprises a lightemitting diode.
 4. An arrangement as defined in claim 1, and furtherincluding switch means for connecting said energy-storing means incircuit with said supply means and said photosensitive means in responseto opening of said shutter.
 5. An arrangement as defined in claim 4,wherein said switch means is mechanically connected with said shutter.6. An arrangement as defined in claim 4, wherein said switch means ismechanically connected with the shutter-activating means.
 7. Anarrangement as defined in claim 1, wherein said photosensitive meanscomprises a photoresistance whose resistance decreases with increasingintensity of impinging light and at a lesser rate when the lightintensity is higher and at a higher rate when the light intensity islower.
 8. An arrangement as defined in claim 1, wherein saidenergy-storing means comprises a capacitor.